Magnetic recording medium comprising a polyester film substrate, a magnetic coating and a specified back coat layer

Abstract

Disclosed herein is a magnetic recording medium comprising a polyester film layer, a coating type magnetic layer provided on one side of said polyester film layer, and a back-coat layer provided on the other side of said polyester film layer.

What is claimed is: 
     
       1. A magnetic recording medium comprising a biaxially stretched polyester film layer, a coating magnetic layer on one side of said polyester film layer, and a back-coat layer formed by an in-line coating method on the other side of said polyester film layer, which is prepared from a composition comprising an aqueous polymer containing 10-60 wt. % of at least one type of fine particle having an average particle diameter of 0.01 to 0.5 μm, selected from the group consisting of carbon black particle, aqueous fluorine polymer particle and synthetic calcium carbonate particle; the thickness of said back-coat layer being 0.2 to 1.5 μm, the center line average roughness (Ra) of said back-coat layer being 0.015 to 0.10 μm; wherein the average particle diameter of said carbon black particle is 0.01 to 0.20 μm; wherein the average particle diameter of said aqueous fluorine polymer particle, when present, is 0.05 to 0.3 μm; wherein the content of said carbon black particle in said back-coat layer, when present, is 10 to 50 wt. %; and wherein the content of said aqueous fluorine polymer particle, when present, in said back-coat layer is 0.1 to 20 wt. %. 
     
     
       2. A magnetic recording medium according to claim 1, wherein said aqueous polymer is an aqueous polyurethane or aqueous polyester. 
     
     
       3. A magnetic recording medium according to claim 2, wherein said aqueous polyurethane is a polyurethane having an anionic group. 
     
     
       4. A magnetic recording medium according to claim 2, wherein said aqueous polyester is a polyester having an anionic group.